Buysellads.com (BSA) is a banner advertisement program which was found in 2008. You would have seen many sites with an independent page for Advertise here or something similar. Such options can mostly been seen on popular sites with tons of views each day.
But what if you don't get any advertisers through such Advertise here pages.Thats what BuySell ads for. It helps webmasters to place third party ads on their blogs/websites. They have some fixed ads banner sizes like (125 x 125, 300 x 250, 728 x 90) and you can make places for these dimensions on your blog and place Buysell ads at them.
This is a general idea of it. Getting approved by them is a bit tricky. I would say its hard for those who don't get decent amount of views. Once you have the audience you would be having so many different ways to earn online but you really need to "build" you blog for that first.
Their are different ads types available to. Like Image only, Image + text, only text etc. You can control the price of each ad unit on your blog and once you get around 50$ you are eligible to be paid. They pay you via PayPal.
The minimum earnings from an ad unit is 10$. If you are a beginner you can start from here on and once you feel your blog is build up you can increase the rates.
Applying for Buy Sell ads is quite simple and you just have to fill their form. Try out this great opportunity and hopefully you would get approved.
If you believe your blog is in early stage i would recommend that you should concentrate on building content for your blog and once it have a strong backbone then you can look forward to make money with it.
Hope that was helpfully.